A hook-and-loop fastener is a well know fastener type and wildly adapted in a variety of fields that need to fasten two articles together, such as garment, hats/caps, sporting goods, etc. A hook-and-loop fastener mainly consists of a hook strap on which a plurality of plastic hooks are formed and a loop strap on which a plurality of fabric loops are formed and by engaging/disengaging the hooks on the hook strap and the loops on the loop strap, a fastening/unfastening function is provided.
FIGS. 1a and 1b illustrate a method for making a hook strap which generally includes: providing thermoplastic resin 1 into a plastic extruder 2; extruding melted thermoplastic resin 1 from the extruder 2 into a plurality of die cavities 4 formed in an outer periphery of a molding roller 3; cooling the molding roller 3 to form a hook strap 7 on which a plurality of upstanding stems 6 are molded; striping the hook strap off the molding roller 3 by a stripping roller 5; and feeding the hook strap through a nip formed between a pair of shaping rollers and the shaping roller that contacts the stems heats the free end of the stems to a temperature above a flow point of the thermoplastic reason to shape the stems into hooks with desired shape.
FIGS. 2 and 3 illustrate the structure of two existing mushroom-type hook strap respectively, wherein FIG. 2 shows an array of circular-headed mushroom-type hooks (FIG. 2b) that are formed from cylindrical stems (FIG. 2a); and FIG. 3 shows an array of elliptic-headed mushroom-type hooks (FIG. 3b) that are formed from tetragon stems (FIG. 3a). Although these two mushroom types of hooks both may provide certain fastening/unfastening function, they both have their own deficiencies. For instance, when engaging the circular-headed mushroom-type hooks illustrated in FIG. 2 with the fabric loops on the loop strap, the effective engaging percentage is relative low because the smooth periphery of the circular head of the hooks does not provide protruding portions that can engage with the fabric loops, and thus has a drawback of unable to provide sufficient fastening strength. Additionally, circular-headed mushroom-type hooks can provide effective engaging only when the head of the hooks fully inserted into the fabric loops forming a lockup type engagement. However, although this lockup type of engagement may provide a firm engagement, the fabric loops usually will be destroyed by the hooks during a detaching operation between the hook strap and the loop strap, and after several times of engaging/detaching operations the fastening capability will drop sharply or even loosing the fastening capability because the percentage of the loops been destroyed increases as the engaging/detaching operation number increases. As a result, the effective lifetime of this circular-headed mushroom-type hooks is relative short.
Although the ends of the major axis of the elliptic-headed mushroom-type hooks illustrated in FIG. 3 can form effective engagement with the fabric loops and thus can provide higher engagement percentage and larger fastening strength than above-mentioned circular-headed mushroom-type hooks, however, because this type of hooks form effective engagement with the fabric loops only at the ends of the major axis of the elliptic head, the effective fastening strength is provided only in a direction parallel the major axis of the elliptic head. The effective engagement with the loops in a direction perpendicular to the major axis of the elliptic head is much less than in the parallel direction. In other words, the fastening function provided by this type of hook-and-loop fastener is not an all-directional uniform fastening function, but a directional fastening function. Therefore, when the engagement between this type of elliptic-headed mushroom-type hooks and the loops is subjected to an external impact force in a specific direction (such as in a direction perpendicular to the major axis of the elliptic head), an unintentional disengaging may occur and pose a insufficient reliability problem to this type of hooks.
In view of the above-mentioned disadvantages/problems associated with the existing mushroom-type hook strap, there exists a need for a method for making a mushroom-type hook strap which has a higher engaging percentage with the loop strap, has a longer lifetime, and is capable of providing a reliable and all-directional uniform fastening function.